The invention relates to a single-track motor vehicle with an internal combustion engine with at least one cylinder which is arranged in an inclined manner approximately horizontally against the driving direction, with at least one intake valve being arranged above at least one exhaust valve. Single-track vehicles within the terms of the invention are motorcycles or snowmobiles with a drive track through which the propulsion force is transmitted.
It is common practice in motorcycles whose engine comprises a crankshaft which is disposed transversally to the driving direction to dispose the cylinder(s) in an upright manner or in a forwardly inclined manner as seen in the driving direction. Generally, the gear is disposed in this case behind the engine and in front of the rear wheel, thus allowing the representation of a favourable power transmission. In motorcycles which are equipped with a low step-through in the form of a motor scooter, there are problems which are difficult to solve in such a design, particularly when engines of higher piston capacity are provided. In particular, an infinitely-variable change-speed gear, which is known as a so-called Variomatic, poses particular packaging problems.
Similarly, in snowmobiles with more powerful engines there are problems housing the engine and the gear in the space below the front bonnet.
A cross-country motorcycle is known from DE 36 01 273 A which is provided with a cylinder which is arranged rearwardly in a substantially horizontal manner. This arrangement is used in the known solution to achieve the longest possible rear suspension swing arm, thus improving the performance. In the illustrated cross-country motorcycles, an additional load on the front wheel by an engine disposed forwardly as far as possible is advantageous.
It is the object of the present invention to house the drive unit of a single-track motor vehicle in a particularly compact and space-efficient manner. In contrast to the aforementioned state of the art, it is intended to provide an engine in a motorcycle which is designed in a particularly short way so as to limit the foot space as little as possible and to achieve the shortest possible wheel base. Similarly, the most compact possible arrangement of the drive unit and a low center of gravity are to be achieved in a similar way in a snowmobile.
This is achieved in accordance with the invention in such a way that the exhaust valve is triggered by a rocker lever. In connection with the cylinder which is arranged in a rearwardly horizontal manner this allows a particularly advantageous intake arrangement in a motorcycle, and in particular, a shifting of the cylinder head close to the rear wheel. The triggering of the exhaust valve(s) via the rocker lever further allows reduction in the overall height of the cylinder head in the zone of the closest approach to the rear wheel. In an analogous manner, it is thus possible to achieve a highly compact engine arrangement in a snowmobile, with the cylinder head of the internal combustion engine coming to lie directly before the drive track.
It is particularly advantageous in this connection when the intake valve is triggered directly by an overhead camshaft. Due to the higher arrangement of the intake valve it is possible to provide an overhead camshaft without any conflict with the rear wheel.
A particularly favourable intake arrangement is achieved when the valves are inclined in a V-shaped manner with respect to one another and when an intake port is guided between the valves to the cylinder. This concerns a so-called reverse tumble arrangement in which a swirl is provided in the combustion chamber whose axis is substantially perpendicular to the cylinder axis.
In a particularly favourable embodiment of the invention an infinitely-variable change-speed gear is provided with a first gear shaft which is in connection with the crankshaft, and with a second gear shaft which is held in the cylinder block of the internal combustion engine. A particularly compact arrangement can be achieved with the arrangement of the drive system in accordance with the invention. It is particularly advantageous in this connection when a centrifugal clutch is held on the second gear shaft. Generally, the centrifugal clutch will be provided on the opposite side of the gear. The infinitely-variable change-speed gear can be arranged as a dry-running pulling strap drive or with a thrust link chain which runs dry or in an oil bath.
An increase in the driving convenience can be achieved in such a way that at least one mass balancing shaft is integrated in the housing of the internal combustion engine.
A particularly compact arrangement of the motorcycle can be achieved when the internal combustion engine is a two-stroke engine with four valves per cylinder.
The production of the internal combustion engine can be simplified substantially when a crankshaft axis, an axis of a differential gear shaft and an axis of the gear shaft are disposed in a common plane of division of the internal combustion engine.
In the arrangement of the invention as a scooter, it is advantageous when the internal combustion engine is a part of the rear suspension swing arm. This means that the rear wheel is held in a drive set swing arm.
The invention will now be explained in greater detail by reference to the embodiments shown in the drawings.